In our U.S. Pat. No. 3,501,605 issued Mar. 17, 1970 there is disclosed a fluid responsive switch utilizing a pivoted arm passing through a bore in a wall of a fluid chamber through which fluid such as a liquid passes. The primary function of the arm is to transmit a force generated within the fluid chamber through a wall of the chamber to the outside. This force when transmitted to the exterior of the chamber wall can be used to operate a micro-switch and thus provide a signal should the fluid flows deviate from a given flow rate. The same type of pivoted arm structure could be used in liquid level indicators to indicate a deviation in a liquid level.
In all such applications, the seal separating the interior and exterior of the chamber through which the pivot arm extends, is an extremely critical element. It must form a flexible water and/or air tight seal at the various pressure differentials, over extended temperature ranges for a wide variety of corrosive and non-corrosive fluids.
In the past, as in the case of our above-referred to United States Patent, such sealing is accomplished by a molded elastic collar configuration. In the prior art structures, metal bellows have been utilized, magnetic couplings, bending tubular type beams and the like.
While many of the foregoing prior art systems have been satisfactory, problems have arisen particularly when the liquid involved is contaminated; that is, including sludge, metal chips and the like. Such particles tend to restrict movement of the pivot arm in which event the rocking action of the arm will be impeded. The sensitivity of the device is thus affected.